1. Field of the Invention
This invention relates generally to radio frequency communication; and more particularly to enhancements in performance and functionality to Radio Frequency Identification (RFID) systems.
2. Description of Related Art
A key application of the disclosed methods is for identification, localization and tracking of tagged assets. An asset is any item whose location is of interest, and an asset tag is a tag associated with the asset, for example, by affixing the asset tag to the asset. Assets may be inanimate objects such as books, or persons, animals, and/or plants. A reader is any device that communicates with the tag.
In a conventional radio frequency identification (RFID) system, data encoded in a tag is communicated by the tag to a reader in response to a query from the reader. A tag may be batteryless (i.e., a passive tag), in which case a transmitted beam from the reader energizes the tag's circuitry, and the tag then communicates data encoded in the tag to the reader using modulated backscatter. Since the tag is typically affixed to an asset (e.g., an item being tracked by the RFID system), the data encoded in the tag may be used to uniquely identify the asset.
In the case of a semi-passive tag, a battery included with the tag powers the tag's circuitry. When the tag detects the transmitted beam from the reader, the tag communicates data encoded in the tag to the reader using modulated backscatter. In the case of an active tag, a battery included with the tag may power the communication to the reader without first detecting or being energized by the transmit beam. Semi-passive tags and active tags may also include data encoded in the tag that may uniquely identify the asset.
In conventional RFID systems, the ability of the reader to determine the location of a tag may be limited because the reader typically transmits a beam with a broad pattern. Conventional RFID systems may employ a reader including one or more antennas, where each antenna has a fixed beam pattern. These antennas are typically separated by a spacing that is large compared to the transmitted beam's wavelength, in order to provide diversity against multi-path fading and to increase the reliability of receiving the communication from tags with unknown orientations. In addition, conventional RFID systems may be limited when the communication range between a single fixed reader and a tag is too small to read all tags in an area of interest.
Active tags are equipped with batteries, and can communicate with readers in an arbitrary format. In particular, unlike passive and semi-passive tags, active tags can also initiate communication. In all cases, the communication between readers and tags is governed by a prespecified protocol, and the assumption in most systems is that all nodes in the system are actively communicating based on such a protocol. Examples of active tags are “WiFi” tags that are compatible with the IEEE 802.11 wireless local area network (WLAN) standards. The use of such tags allows potentially exploiting existing WLAN infrastructure for asset identification, localization and tracking.
All references cited herein are incorporated herein by reference in their entireties.